Vol.4, # 6
February 10, 2007

Q: What is konjac mannan and what is it good for? - Layperson

A: Scientific Name: Konjac mannan
Other Names: Amorphophallus konjac, Devil's Tongue, Elephant-foot Yam, Glucomannan, Konnyaku, Snake Plant

In parts of Asia, individuals slice and fry fresh glucomannan tubers like potato chips. More frequently, the tubers are shredded, dried, and ground to make a grainy meal or a powdery flour, which is often used to make noodles. Glucomannan meal or flour may also replace part of the corn meal, wheat flour, or rice flour used in cooking and baking. Mannose, a sugar extracted from glucomannan, is sometimes substituted for sugar in products for individuals with diabetes. In Japan, a popular type of jelled candy called konnyaku is made from glucomannan. A liquid form of glucomannan has been tested as a preservative to control bacteria that may contaminate other foods. Powdered glucomannan is used to thicken cosmetics, foods, and pharmaceuticals. Since it is broken down and absorbed in the colon instead of in the upper digestive tract where most other foods are digested, glucomannan is being studied as a way to deliver drugs to the large intestines to treat conditions such as irritable bowel syndrome. It has also been included in artificial skin products that are used to cover large wounds and promote healing.

Who is this for?


Glucomannan is the Western name for vegetable fibers derived from an Asiatic plant family known as konjac. Glucomannan does not dissolve in water, but forms a thick, gooey gel when exposed to fluids. The body does not digest glucomannan, so the resulting large soft mass moves through the intestines and may trigger intestinal muscle contractions. Therefore, glucomannan is thought to be an effective bulk-type laxative, even though it may take up to 12 hours to be effective.

Glucomannan has also been studied for treating obesity, diabetes, and high cholesterol. Studies in both adults and children with severe obesity showed varying degrees of weight loss associated either with taking supplemental glucomannan or with replacing some of the usual diet with foods made from glucomannan (konjac) flour – the dried and ground tuber (underground stem) of the plant. Generally, it is believed that glucomannan discourages overeating because it creates a feeling of fullness that persists because the fiber in it swells Therefore, stomach contents stay in the stomach longer. However, in most of the research studying glucomannan for weight loss, participants also drank increased quantities of water and followed a reduced-calorie diet.

Possibly due to the same delay in stomach emptying, glucomannan may improve blood sugar levels in individuals with diabetes. Because the absorption of carbohydrates from foods is slower when glucomannan is taken, blood sugar levels may not rise as high or as fast as usual. Some preliminary results from animal studies also suggest that glucomannan may increase the sensitivity of body tissues to the insulin that is produced or taken. In several studies, taking glucomannan has also appeared to lower blood levels of total cholesterol, low-density lipoproteins (LDL, or "bad" cholesterol), and triglycerides. Although more research on this possible use of glucomannan is needed, it is believed that glucomannan may increase the elimination of cholesterol and its components from the body. It may also keep bile acids from being reabsorbed in the intestines, further reducing cholesterol levels in the blood, because the body uses cholesterol to produce more bile.


Although glucomannan has been studied in children as young as 5 years old, very little information is available on how glucomannan might affect a developing fetus, an infant, or a small child. Therefore, its use is not recommended during pregnancy, while breast-feeding, or before the age of 5.

Individuals with diabetes should avoid using large amounts of glucomannan because it may lower blood sugar levels, potentially resulting in hypoglycemia (blood sugar that is too low). Symptoms of low blood sugar include shakiness, sweating, confusion, distorted speech, and loss of muscle control. If not corrected, low blood sugar can lead to unconsciousness and even death.

What side effects should I watch for?

Glucomannan tablets are not recommended for oral use. Reportedly, several individuals experienced blockage of the esophagus when they took glucomannan in tablet form. The tablets lodged in their throats and swelled when exposed to water. Although no cases have been reported, the potential for a similar blockage of the intestines exists.

One case of allergic pneumonia caused by inhaling glucomannan dust has been documented in an individual who worked for over 35 years in a factory that produced glucomannan powder.

What interactions should I watch for?

Glucomannan's possible lowering effect on blood sugar may intensify the effects of insulin and oral drugs for diabetes, such as:

  • Actos
  • Avandia
  • glimepride (Amaryl)
  • glipizide (Glucotrol XL)
  • glyburide (Glynase)
  • Glyset
  • metformin (Glucophage)
  • Prandin
  • Precose

When mixed with water or other fluids, glucomannan forms a sticky, slippery gel that may coat the stomach and intestines. In theory, taking glucomannan by mouth could block the absorption of drugs, herbal products, other dietary supplements, or nutrients from foods that are taken at the same time. Those who take glucomannan should not take drugs, herbals, or dietary supplements within 2 hours.

Because glucomannan may decrease blood sugar levels, taking it with other blood sugar-lowering herbal products may result in hypoglycemia -- blood sugar that is too low. Herbals that may reduce blood sugar include:

  • Eleuthero
  • Fenugreek
  • Ginger (in high amounts)
  • Kudzu
  • Panax Ginseng

American and Korean red ginseng may help to normalize blood glucose levels and improve insulin secretion and sensitivity in patients with type 2 diabetes, two new studies suggest. University of Toronto investigators presented both trials here this weekend at the American Diabetes Association 63rd Scientific Sessions.

In one study, people with type 2 diabetes who consumed ginseng and Konjac mannan fiber (a highly viscous fiber similar to pectin) had a notable reduction in blood glucose levels, reported Alexandra Jenkins, BSc, RD, a research associate at the University of Toronto in Ontario.

The double-blind, placebo-controlled, crossover-designed study enrolled 30 well-controlled diabetes patients; 23 were receiving oral hypoglycemic agents, and seven used lifestyle intervention alone. The participants, who were kept on their standard diabetes regimen, were randomly assigned to receive either 3 g of ground-up North American–grown ginseng and 7 g of Konjac mannan fiber blend, or placebo, daily for 12 weeks.

By the end of the study period, hemoglobin A1c (HbA1c) levels had dropped from an average baseline level of 7.0% to 6.5% in patients were taking the ginseng preparation compared with 6.8% for those who were taking placebo, Ms. Jenkins said.

"The drop is comparable to that seen with other hypoglycemic agents, such as the alpha-glucosidase inhibitors, when used as adjunct therapy," she said. The herbal preparation appeared to be safe, with no adverse effects observed, she said.

The results suggest that standard pharmacological therapies and ginseng are complementary in treating diabetes, said Francine R. Kaufman, MD, outgoing president of the American Diabetes Association. "The Chinese, who use ginseng root to treat a variety of ailments, have been in medicine for 5,000 years," she said. "Just as acupuncture has been proven to have a role in Western medicine, so too will ginseng. We need to think globally."

In the second study, Korean red ginseng improved both insulin secretion and insulin sensitivity when compared with placebo, reported John L. Sievenpiper, a PhD candidate at the University of Toronto. The trial enrolled 19 well-controlled diabetic patients, applying the same design used in the American ginseng study.

Korean red ginseng was safe, with liver, kidney, and hemostatic function and blood pressure not adversely affected compared with placebo, the study showed.

While HbA1c levels did not significantly change, the ginseng preparation "was associated with a dramatic 40% drop in both postprandial plasma glucose and insulin levels," Mr. Sievenpiper said. Also, ginseng treatment led to a significant improvement in both hepatic insulin sensitivity and whole-body insulin sensitivity compared with placebo, he reported.

"The baseline HbA1c levels were already at 6.5%, so we couldn't push it down significantly," he said. "But in patients with slightly higher levels, we might see an effect."

Dr. Kaufman, who is also head of the Center for Diabetes at Children's Hospital in Los Angeles, California, agreed. "There is no doubt that natural products such as ginseng have a role in modulating weight and insulin sensitivity," she said. But exactly "how adjunctive they may or may not be" still needs to be determined, she added.

Mr. Sievenpiper emphasized that "these are preliminary, short-term studies that indicate a need for more research. They are not a reason to recommend ginseng to patients," he said. And because of poor regulation, standardization, and labeling in the herbal industry, there is no way to know if one product will work as well as another, Mr. Sievenpiper said.

He pointed out that in a recent survey physicians estimated that three in four patients take complementary medicines, including herbs. Therefore, physicians should ask their diabetes patients if they are taking ginseng or other complementary therapies, because standard medication dosing may need to be adjusted.

The Korean red ginseng study was funded in part by the Korean Ministry of Agriculture and Forestry.

Some interactions between herbal products and medications can be more severe than others. The best way for you to avoid harmful interactions is to tell your doctor and/or pharmacist what medications you are currently taking, including any over-the-counter products, vitamins, and herbals.  

Should I take it?

Glucomannan is a plant that grows mainly in Asia where it is known as konjac. A closely related species is known as elephant-foot yam due to the exceptionally large tuber (an enlarged underground extension of the plant stem) that it produces. Each glucomannan plant produces one large tuber similar to a beet. Unlike most plants with roots that extend from the bottom of the tuber, glucomannan's roots grow from the top of the tuber, which also puts out one thick stem. Each glucomannan stem in turn, has only one leaf. A single, large, showy, but foul-smelling flower may bloom before the leaf appears. Depending on the species, the leaf may be multi-lobed or single. Glucomannan may be called snake plant because blotchy green, white, yellow, and/or brown markings on the stems resemble snake skin. Tubers, which are usually harvested in the autumn from three-year old plants, can grow up to 10 or more pounds.

Dosage and Administration

Note: Taking glucomannan tablets has been associated with occasional life-threatening blockages of the throat. Individuals who decide to use it should either take capsules and swallow them with plenty of water or use a glucomannan powder that is mixed into fluids before swallowing. Glucomannan should always be taken with 8 ounces or more of water or other fluid.

Common doses used in studies have included:
Use Dose Frequency
Laxative 3,000 mg to 4,000 mg (3 grams to 4 grams) Once. Repeated after 12 hours, if necessary
Diabetes 3,600 mg to 7,200 mg (3.6 grams to 7.2 grams) Once a day
High Cholesterol 3,900 mg (3.9 grams) Once a day
Weight loss (Adults) 1,000 mg (one gram) Three times a day
Weight loss (Children) 700 mg to 1,000 mg (0.7 grams to one gram) Three times a day


Glucomannan, the fiber obtained from the tubers of the konjac plant, is used mainly as a laxative. It may also encourage weight loss, help to lower blood sugar levels, and lessen cholesterol in the blood.


Individuals with diabetes should not take glucomannan due to possible changes in blood sugar that it may cause. Children under the age of 5 and women who are pregnant or breast-feeding may want to avoid using glucomannan, as well.

Side Effects

In tablet form, glucomannan has been associated with esophageal blockages.


Glucomannan's potential decreasing effect on blood sugar may increase the effects of drugs or herbs that also lower blood sugar.

GLUCOMANNAN may interact with METFORMIN (in Glucophage) and INSULIN

Taking glucomannan may lower blood sugar levels. However, it may also delay or block the absorption of oral drugs by the body. When glucomannan is used together with oral drugs like metformin  and injectables like insulinthat also reduce blood sugar levels, blood sugar may get too low--a condition called hypoglycemia. Signs of blood sugar that is too low may include feeling weak or shaky, having a headache, or being confused or nervous. On the other hand, if glucomannan blocks the effects of metformin, blood sugar may not be lowered adequately. If glucomannan and metformin are taken together, they should be separated by as much time as possible - at least several hours. Blood sugar may still become unpredictable. Therefore, individuals who take glucomannan, metformin, and/or insulin should monitor blood sugar levels more closely than usual. Those who experience problems may need to stop taking glucomannan. Discuss this potential interaction with your healthcare provider at your next appointment, or sooner if you think you are having problems.

This interaction is well-documented and is considered moderate in severity.

In short, Konjac mannan and Konjac mannan/Ginseng combinations have produced remarkable improvements in in the blood sugar levels of Type I and Type II Diabetics (more so in Type II). Some Type II diabetics no longer require medication and enjoy less restrictive diet and exercise regimens. For the best results, use only standardized supplements and continue to follow a healthy diet and exercise regimen and consult  the proper healthcare professional familiar with their use


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DISCLAIMER:  The information in this column, is NOT intended to diagnose and/or treat any health related issues and is provided solely for informational purposes only. Consult the appropriate healthcare professional before making any changes to your healthcare regime. Even what may seem like simple changes in the diet for example, can interact with, and alter, the efficiency of medications and/or the body's response to the medications. Many herbs and supplements exert powerful medicinal effects. Neither the author, nor the website designers, assume any responsibility for the reader's use or misuse of this information.

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